Crystal structure analyses of the three oxidation states of flavodoxin, an electron-transferring flavoprotein from Clostridium MP, are to be completed at high resolution (1.9 - 2.5 A) by isomorphous replacement followed by refinement. Results from the refinement will be used to determine the extent of conformation change accompanying the oxidation-reduction reactions, and to elucidate the basis for the shifts in oxidation-reduction potential of FMN resulting from combination of FMN with the apo-protein. Deductions from spectral measurements on solutions and crystals will be compared with the molecular models produced by crystallographic analysis. Structures of related small molecules may also be determined.